Safety belt pretensioner

Abstract: In a safety belt pretensioner, the safety belt (22) can be tightened around a passenger under the action of a cable (24) pulled by a piston (36), in a cylinder (26), driven by expanding gas from a gas generator (32). To reduce the length of travel of the piston (36) necessary to achieve sufficient tightening of the belt, and hence reduce the total size of the device, the cable (24) is passed over a pulley (40) attached to the piston (36), and also over a fixed pulley (46). On detection of a sudden deceleration the gas generator (32) is activated. Gas from the generator (32) drives the piston (36) along the cylinder (26). The cable (24), one end of which (60) is anchored to the cylinder, is then pulled over the two pulleys (40,46), causing a drum (18), onto which the second end of the cable (24) is anchored, to rotate in direction A. The rotating drum (18) engages the belt take-up shaft (20) in rotation via a clutch mechanism (19,19A,21). The safety belt (22), which is wound onto the shaft (20), is thereby tightened.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a pretensioner according to the upper portion of claim 1, which is used in a webbing take-up device, and which causes a webbing to be applied closely to a vehicle occupant when a vehicle suddenly decelerates. Description of the Related Art A seat belt device must insure the safety of a vehicle occupant by tightly restraining the vehicle occupant by a webbing when the vehicle suddenly decelerates. The pretensioner is designed such that the webbing can be freely taken up or pulled out without any interference with the rotation of the take-up shaft during ordinary running of the vehicle. When the vehicle suddenly decelerates, the take-up rotary force of the pretensioner is transmitted to the take-up shaft of the webbing by a clutch mechanism provided between the take-up shaft and the pretensioner, so that the webbing is taken up in the direction which restrains the vehicle occupant. The take-up rotary force of such a pretensioner is obtained in the following manner. A gas is fed under pressure into a cylinder so that a piston is caused to move suddenly, thus causing instantaneous rotation of a rotating drum around which a wire, one end of which is connected to the piston, is wound. The rotary force of the rotating drum is transmitted to the take-up shaft of the webbing by the clutch mechanism. A pretensioner of the kind previously described is known from DE 30 40 667 A1 and WO 89/01430. The movable pulley of the respective pretensioner arrangements are disposed on a respective piston rod extending to outside of the cylinder therefore requiring a large attachement and operating space. Summary of the invention In view of the afore mentioned, the object of the present invention is to provide a pretensioner of the art previously described which requires a reduced attachement space and which is more compact and less expensive than known pretensioners. This object is achieved by a pretensioner having the features of claim 1. In the pretensioner of the present invention, when the vehicle suddenly decelerates, a large amount of gas is generated and the gas flows into the cylinder. Due to the pressure of the gas, the movable pulley moves instantaneously together with the piston, so that the wire trained around the movable pulley is pulled. The amount by which the wire is pulled is twice the amount by which the wire is pulled in cases where the wire is directly connected to the piston, as in conventional devices. Accordingly, the same amount of wire can be pulled with half the length of a conventional cylinder, thus making it possible to manufacture a pretensioner which has a short cylinder. Further, since the pressure of the gas is received by the bottom surface of the piston and does not act on the movable pulley, the movable pulley, which is axially supported in slots formed in side walls of the piston, can rotate smoothly without being affected by the gas pressure. When the wire is pulled, the rotating drum around which the wire is wound rotates, and the rotary force is transmitted to the take-up shaft via the clutch mechanism, so that the webbing is tensed in the direction which restrains the vehicle occupant. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded perspective view which illustrates a pretensioner of the present invention. Fig. 2 is a cross section of the pretensioner during normal running of the vehicle. Fig. 3 is a cross section of the pretensioner during sudden deceleration of the vehicle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows a webbing take-up device 12 equipped with a pretensioner 10 of the present embodiment. The webbing take-up device 12 has a frame which is formed from a rectangular plate 14 and a pair of leg plates 16 which are bent at right angles from the sides of the plate 14 so as to be parallel to each other. The leg plates 16 axially support both ends of a take-up shaft 20 such that the take-up shaft 20 is rotatable. The tip end of a webbing 22 applied to a vehicle occupant is engaged with the take-up shaft 20, and the webbing 22 is wound in a roll form on the take-up shaft 20. A rotating drum 18 which is positioned on the outside of one of the leg plates 16 is coaxially connected to one end of the take-up shaft 20 via a clutch mechanism 23. A wire 24 is wound around the rotating drum 18, and an end portion of the wire 24 is fixed to the rim portion 18A of the rotating drum 18. When the rotating drum 18 begins to rotate, the clutch mechanism 23 is actuated so that balls 21 are sandwiched between a central shaft 20A of the take-up shaft 20 and narrow-width portions 19A of a cam groove 19 formed at a shaft portion of the rotating drum 18, so that the take-up shaft 20 rotates together with the rotating drum 18. Further, a cylinder 26 is attached alongside the webbing take-up device 12. The cylinder 26 is a rectangular tube which is open at one end and which has a bottom portion 28 at the other end. A guide passage 34 which communicates with a gas-generating device 32 is connected to a circular hole 30 formed in the bottom portion 28. A gas-generating agent (enhancer or the like) and a detonator, which are not shown in the drawings, are accommodated in the gas-generating device 32. When an acceleration sensor detects the sudden deceleration of the vehicle, the detonator is detonated, and the gas-generating agent is caused to react by the resulting spark so that a large quantity of gas is generated. Further, a box-shaped piston 36, which has an opening 35 provided at the top and which has a bottom surface 36A, is disposed inside the cylinder 26. Slots 38 are formed along side walls 36B from the opening 35. Shaft portions 42 which protrude from sides of a movable pulley 40 are axially supported in the slots 38 such that the shaft portions 42 are rotatable. An intermediate portion of the wire 24 which is wound around the rotating drum 18 is trained on the movable pulley 40. The direction of movement of the wire 24 is changed by means of a fixed pulley 46 which is axially supported by a shaft 44. The wire 24 is passed through a through-hole 48 formed in the bottom portion 28 of the cylinder 26, and is trained over the movable pulley 40. The wire 24 is then passed through a through-hole 58 formed in the bottom portion 28, and is fastened to the cylinder 26 by a stopper 60 (see Fig. 2). Next, operation of the pretensioner 10 of the present embodiment will be described. As is shown in Figure 2, the piston 36 is positioned at the bottom portion 28 of the cylinder 26 during ordinary running of the vehicle. In this case, the take-up shaft 20 is not connected to the rotating drum 18 by the clutch mechanism. Accordingly, the take-up shaft 20 rotates freely so that the webbing 22 can be taken up or pulled out. When the vehicle suddenly decelerates, the acceleration sensor of the gas-generating device 32 reacts so that the detonator is detonated, and the gas-generating agent is caused to react by the resulting spark so that a large quantity of gas is generated. The gas flows into the cylinder 26 via the guide passage 34 and instantaneously pushes the movable pulley 40 upward together with the piston 36. In this case, since the gas is received by the bottom surface 36A of the piston 36 and does not directly contact the movable pulley 40, the movable pulley 40 can rotate smoothly without being affected by the gas pressure. As a result, the wire 24 is pulled into the cylinder 26 so that the rotating drum 18 rotates in the direction indicated by arrow A in Fig. 3. When the rotating drum 18 rotates, the clutch mechanism is actuated so that the rotary force of the rotating drum 18 is transmitted to the take-up shaft 20, thus causing the take-up shaft 20 to rotate integrally with the rotating drum 18. As a result, the webbing 22 can be forcibly tensed in the direction which restrains the vehicle occupant. Thus, as a result of the use of the movable pulley 40, the amount by which the wire 24 is pulled in is twice the amount by which the wire 24 is pulled in cases where the wire 24 is directly connected to the piston 36. Accordingly, even in cases where a short cylinder is used, the take-up shaft 20 can be rotated by the same amount as in the case of a conventional long cylinder.

Claims: A pretensioner which has a cylinder (26) and a piston (36) movably disposed in said cylinder (26) and one end of a wire (24) is connected to a rotatable drum (18) and rotating force of said rotatable drum (18) is transmitted via a clutch mechanism (23) to a take-up shaft (20) of a webbing take-up device (12) when a vehicle suddenly decelerates and said wire (24) due to the driving force of a gas generating device transferred to the piston (36) transmits rotating force to said rotatable drum (18) and rotating force of said rotatable drum (18) is subsequently transmitted to the take-up shaft (20) so as to rotate the take-up shaft (20) to take up webbing, and further comprising: a movable pulley (40) disposed to said piston (36) to simultaneously move with said piston (36), and around which an intermediate portion of said wire (24) is wound characterized in that the piston (36) is box-shaped and has an opening (35) formed by side walls (36B) and a bottom surface (36A), that the movable pulley (40) is disposed inside the cylinder (26) within the opening (35) of the piston (36) with shaft portions (42) protruding from sides of the movable pulley (40) and being supported in the side walls (36B), and that the wire (24) is passed through a through-hole (48) formed in the bottom portion (28) of the cylinder (26) and is guided over the movable pulley (40) and is fastened to the bottom portion (28) of the cylinder (26). A pretensioner according to claim 1, wherein the one end portion of said wire (24) is fixed to a portion of said cylinder (26). A pretensioner according to claim 1 or 2, wherein portions of said wire (24) before and after a portion wound around said pulley (40) are parallel to each other, and disposed within said cylinder (26). A pretensioner according to claim 3, wherein among said parallel portions of said wire (24), the parallel portion, which is the intermediate portion of said wire (24) nearest to the take-up shaft (20), passes through an opening in said cylinder (26) to the outside of said cylinder (26). A pretensioner according to claim 4, wherein the intermediate portion of said wire (24) nearest to the take-up shaft (20) passes through a bottom wall of said cylinder (26) to the outside of said cylinder (26). A pretensioner according to claim 4 or 5, wherein an intermediate portion of said wire (24) between said clutch (23) and said cylinder (26) is wound around a fixed pulley (46). A pretensioner according to claim 6, wherein the intermediate portion of said wire (24) between said clutch (23) and said fixed pulley (46) is substantially parallel to an intermediate portion of said wire (24) between said fixed pulley (46) and the pulley (40) within said cylinder (26). A pretensioner according to claim 7, wherein said cylinder (26) is disposed at a side of the take-up device. A pretensioner according to one of the preceding claims claim, wherein respective cross-sectional configurations of said cylinder (26) and said piston (36) are polygonal.

Inventors: ANDO TAKAYUKI, IMAI KEISUKE, KATO KEIICHI, MATSUI KENJI, TERAOKA FUMINORI, ANDO, TAKAYUKI, IMAI, KEISUKE, KATO, KEIICHI, MATSUI, KENJI, TERAOKA, FUMINORI, ANDO, TAKAYUKI C/OK.K.TOKAI-RIKA-DENKI-SEISAKUSHO, IMAI, KEISUKE C/O K.K.TOKAI-RIKA-DENKI-SEISAKUSHO, KATO, KEIICHI, C/O K.K.TOKAI-RIKA-DENKI-SEISAKUSHO, MATSUI, KENJI, C/O K.K.TOKAI-RIKA-DENKI-, TERAOKA, FUMINORI C/O K.K. TOKAI-RIKA-DENKI-
Applicants: TOKAI RIKA CO LTD, KABUSHIKI KAISHA TOKAI RIKA DENKI SEISAKUSHO
Application year: 1994
Main classification: B60R22
IPC codes: B60R22